Nicotine production from polyamine putrescine, a precursor of nicotine, can be produced by two pathways in plants. Putrescine can be synthesized directly from ornithine in a reaction catalyzed by the enzyme ornithine decarboxylase, or can be produced indirectly from arginine in a sequence of reactions initiated by arginine decarboxylase. The first committed step in nicotine biosynthesis is the conversion of putrescine to N-methylputrescine by putrescine N-methyltransferase (“PMT”). N-methylputrescine is subsequently oxidized by a diamine oxidase, and is cyclized to produce a 1-methyl-Δ1-pyrrolium cation, which is subsequently condensed with nicotinic acid to produce nicotine.